Rob Knox (right) had a small part in the latest Harry Potter film
Cast and crew from the new Harry Potter film are to wear white ribbons on their wrists at its world premiere as a mark of respect to murdered actor Rob Knox.
Mr Knox, 18, who played Marcus Belby in the forthcoming Harry Potter and the Half-Blood Prince, was stabbed in Sidcup, south-east London, last May.
He was defending his brother when he was attacked by Karl Bishop, who received four life terms in March.
The film's world premiere is being held in Leicester Square on Tuesday.
Daniel Radcliffe, who plays the teenage wizard in the film, said Knox's death had hit all of the cast.
He said: "I won't pretend I knew him incredibly well, or was his best friend on set, but I knew him and liked him, and what happened to him was obviously tragic and awful."
The Harry Potter film cast are to pay tribute to all knife-crime victims
Co-star Bonnie Wright, who plays Ginny Weasley, younger sister of Harry's best friend Ron, said the cast wanted to show solidarity with all knife-crime victims.
"It's going to be quite a traumatic experience for his family, who've been very supportive of him," she said.
She said the wearing of white ribbons on their wrists was not only for his life but for other families who had experienced knife crime.
The film is the sixth film based on JK Rowling's best-selling books and has director David Yates, who took charge of the last movie, Harry Potter and the Order of the Phoenix, back at the helm.
He said Knox's death was a "waste".
"You are surrounded by young people all day long who bring a great commitment to what they do, and Rob was no different," he said.
"He came in and wanted to do brilliant work, he put his heart and soul into it, and you just think 'what a terrible waste'."
Murdered Potter film star praised